The present invention relates to a method for assisting the reversal of an articulated vehicle by determining a swept area for a vehicle combination, which is used when reversing the vehicle. The method is especially suited for use with a reverse assistance function.
Professional drivers of heavy trucks with trailers often have to manually perform path planning and path following with high precision when rearranging the vehicle combination during low speed. This could for example be when loading or unloading the vehicle, docking at loading bays, parking in tight spaces, coupling trailers or changing swap bodies. During low speed manoeuvres with a long vehicle combination, even an experienced driver must be concentrated, and it may well be both stressful and time consuming.
Reversing a commercial heavy articulated vehicle is a challenging task even for an experienced driver. The driver must concentrate on controlling the steering wheel angle of the vehicle in order to keep the vehicle combination's articulation angles correct such that the desired path can be followed during reversing. Due to this, there is a risk that less attention is given to safety issues through observations of the surrounding around the vehicle to avoid collisions with pedestrians, fixed and moving obstacles. One such situation may be when the driver is maneuvering the vehicle combination with low speed before the delivery of goods or when he has driven into a narrow and tricky road/street by mistake and needs to reverse the vehicle combination back out from this narrow road/street. Another situation could be a timber truck combination which drives into an incorrect small forest road, where turning the vehicle combination around is not possible and reversing the vehicle combination is necessary.
Another typical situation is when the driver is at a known cargo central and wants to start a low speed rearranging procedure to line up with the docking bay. This procedure may have been done by the driver several times before, i.e. the driver will have to manually reverse into the docking station by himself time after time. This means that the driver has to put a lot of effort into using the steering wheel to achieve a significant steer input, especially during reversing since several articulation joints make the vehicle combination hard to control. This will also increase the risk of work related injury of aching shoulders and back which is common for commercial heavy truck drivers.
One way to reduce the work load and stress on the driver when reversing is to provide the truck with a reverse assistance function. The reverse assistance function will assist the driver when reversing the vehicle combination, thereby allowing the driver to focus on supervising the manoeuvre and to monitor the surrounding of the vehicle. The reverse assistance will reduce the time spent during reversing, e.g. the time spent to dock a loading platform, which will increase the productivity of the vehicle and the precision of the docking operation. Further, it may also reduce accidents that could damage both the vehicle combination and surrounding objects since the driver can be fully concentrated on supervising the vehicle motion rather than planning and executing the reversing of the vehicle combination. Another advantage is that also inexperienced drivers will be able to perform difficult low speed maneuvering tasks.
Reverse assistance is becoming increasingly popular by passenger cars, where the control task of the reverse assistant function often uses separate controllers for the steering and for the speed. The driver of the vehicle may e.g. control the reverse speed of the vehicle and the control system of the vehicle controls the steering of the vehicle when parallel parking. The system comprises a speed limit such that the driver can only move the vehicle below the set speed limit. In this way, the steering actuator will be able to follow the desired path and the driver will have time to observe the surrounding.
For a reverse assistance system that is to be used with a heavy vehicle such as a truck, other features are desirable. With a heavy vehicle, parallel parking is not a primary purpose. Instead, reversing over longer distances, e.g. for docking to a loading platform, or for reversing through sharp turns are useful features. Further, the reverse assistance system should also be adapted to handle a vehicle combination comprising a truck and a trailer.
One issue with a reverse assistance function is to keep track of the surrounding of the vehicle combination when reversing. Even if the vehicle is provided with rear mirrors and a back-up camera, there will be areas close to the vehicle that are hidden from the view of the driver, especially for a vehicle having more than one articulation joint. It is of course possible to install more cameras or proximity sensors on the trailers, but the integration of different trailers with the control system of the towing vehicle would be rather complicated. Such a solution could work for a dedicated truck-trailer combination.
It is thus of advantage to provide a method for improving the safety when reversing an articulated vehicle.
It is desirable to provide a method for determining a swept area of a vehicle for a specified path, and to use the swept area when reversing the vehicle along the specified path.
In a method for assisting the reversal of an articulated vehicle, the steps of recording a predefined number of positions for a first articulated vehicle for a specified path, recording the articulation angle of each articulation joint of the articulated vehicle at the predefined number of positions, recording the heading for the first articulated vehicle at the predefined number of positions, saving the recorded values for the specified path in a memory, calculating the swept area of the first articulated vehicle for the specified path by using the recorded values and size information of the articulated vehicle, and using the swept area to control the steering of the articulated vehicle when reversing the articulated vehicle along the specified path, such that the articulated vehicle does not extend outwards of the swept area during the reversal are comprised.
By this first embodiment of the method, the method will first record a predefined number of positions for a first vehicle for a specified path, thereby defining the traveled path. The specified path may e.g. be the last part of a traveled route, or may be a path that has been traveled at an earlier moment. The specified path is saved in a memory. Thereafter, the swept area for the traveled path is calculated. The swept area is the total area covered by a projection of the vehicle on the ground, i.e. a corridor in which the vehicle has been traveling. In order to be able to calculate the swept area, the control unit of the vehicle records values for the articulated vehicle during travel along the specified path and uses stored vehicle parameters for the complete articulated vehicle including equivalent wheel bases, length and width of the towing vehicle and the towed vehicles.
In this way, the articulated vehicle can use the swept area when reversing and the steering of the articulated vehicle can be controlled such that the articulated vehicle does not extend outside of the swept area. It may however be unpractical to control the steering such that the vehicle does not extend outside of the swept area. Due to e.g. the speed of the steering actuator, the speed of the vehicle and noise and resolution of the used sensors, the vehicle may extend outside the swept area to a certain extent. By adding a tolerance band to the swept area, a modified swept area is obtained, inside which the articulated vehicle can remain during reversal. Theoretically, it is possible to set the tolerance band to zero, but a tolerance band in the order of less than 20 cm is of advantage. In this way, the modified swept area is used to control the steering of the vehicle when reversing the vehicle along the specified path, such that the vehicle does not extend outwards of the modified swept area during the reversal.
In this way, the vehicle combination will be controlled such that it is substantially within the swept area during the reversal of the specified path. If the specified path is the last path traveled by the vehicle combination, the driver can be ensured that he can reverse along the specified path without running into any obstacles, since he knows that he has just traveled the same path. Has the driver e.g. driven into a narrow road by mistake, he can reverse along the same road and be confident that he is within the road at all times. This saves time and relieves the driver of a lot of stress, both from the reversing itself and from keeping the vehicle combination on the road. Especially for a relatively long and/or curved road, this is of advantage.
Preferably, the projection of the vehicle combination in the tolerance band of the modified swept area is minimized during the reversal. Depending on different parameters, such as reversal speed, the steering actuator, the used sensors etc, the projection of the vehicle combination can be allowed to extend more or less in the tolerance band. It is preferred to minimize the total area projected in the tolerance band during the reversal since this will give a smoother reversal and a higher security. The width of the tolerance band is set such that a reasonable reversing speed can be used but where the width of the tolerance band is narrow enough to give a good tolerance to obstacles around the vehicle.
In a development of the method, the swept area is saved in a memory and used at a later moment, when the articulated vehicle combination is to reverse into a known location. This may e.g. be a loading dock, into which the driver reversed the vehicle the first time. When driving out of the loading dock, the path is saved. The next time the vehicle is to visit the same loading dock, the reverse assistance function of the vehicle can use the stored path to reverse into the loading dock. The swept area can either be stored in a memory in the specific vehicle or in a central database where different vehicles can access the information. In this way, also vehicles that have not been at a specific position before can use a swept area for a reversal.
In a development of the method, the swept area of a first articulated vehicle combination can be used to assist a second articulated vehicle combination having a different wheel base to reverse along a specified path. It may e.g. be that a second vehicle combination is going to reverse to the same loading dock. The swept area of the first vehicle combination can in this case be used by the second vehicle to reverse into the loading dock. If the difference between the first and the second vehicle combination is relatively large, such that a relatively large tolerance band is needed to assist the reversal of the second vehicle combination, a message may be given to the driver that he should be careful and pay extra attention. This may e.g. be the case if the second vehicle is much wider or longer than the first vehicle. However, normally, the width of different vehicle combinations do not differ much since the width of heavy vehicles is well specified and governed by legislation.
In a development of the method, different swept areas at the same location can be combined in order to create an aggregate swept area. This aggregate swept area may comprise two or more swept areas from previous paths at the same location. Normally, a driver does not always use exactly the same path at e.g. a loading dock. At a normal loading dock, the unloading position may e.g. vary sideways with 1 meter or more. After several vehicles have unloaded at the same loading dock, different swept areas may have been saved for the same location. By combining these swept areas, a wider allowed corridor for the vehicle combination is provided. In such a case, it may not be necessary to use a tolerance band at all.